Wednesday, January 5, 2011

Adventures In Compatibility

With Cervelo's new "BBright" bottom bracket standard comes new challenges in mating drivetrain parts. The BBright layout is similar to the popular BB30 standard in that the crank spindle is 30mm in diameter, but Cervelo has chosen a BB shell width of 79mm instead of the typical 68mm found on road bikes, even those using the BB30 standard.

Interestingly, the drive side of Cervelo's BBright bottom bracket shell is unchanged from a BB30 shell and the extra 11mm in shell width is added to the non-drive side of the frame.

Partering with Cervelo in the BBright project is Rotor, who makes an impressive crank specifically for BBright frames. Unfortunately, Rotor does not offer a BBright crankset with 180mm crankarms. We therefore chose to outfit Tom's new Cervelo R3 with a Shimano Dura Ace crankset, which is offered in 180mm.

The most obvious challenge in using the Shimano crank is to reduce the bottom bracket opening from 30mm to Shimano's 24mm Hollowtech II spindle diameter. This is fortunately achievable using BB30 adapters currently on the market. The problem, however, is that these adapters are made with a 68mm bottom bracket shell in mind and not the BBright 79mm shell.

Because the drive side of the bike follows the BB30 standard, the adapter works fine on the non-drive side. On the non-drive side, however, Colin had to fire up the lathe and turn this:

Into this:

Tom's crank is now spinning happily along. Stock Q-factor is preserved, and it has ample clearance on both sides.

The appropriate adapters should be commercially available at some point, but I could not find them at the time of this post.